L7808 Regulator 19v 20ampere Power Supply

RendiArdian · ‎2025-09-21

I was design 19 volt regulated power supply, but I don't know the exact value for the transistors, and I noticed at the voltsim output didn't reach the maximum 19 volt output, can anyone help me for the solution for my design, regards.

@all

Peter BENSCH · ‎2025-09-21

@RendiArdian

The schematic shows a current regulator that uses the potentiometer as a shunt. However, if your output parameters are actually 19V, 20A (even though you have drawn 1.9V), there would have to be 20,000V at the 1k potentiometer (20A * 1k = 20kV).

Please explain what your schematic is supposed to do or what you are connecting there, because (at least) something about it is not right.

Regards
/Peter

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AScha.3 · ‎2025-09-21

Why using a fixed 8V reg for a 19V supply ?

+

You have planned the cooling ? (need a big heatsink, + fan probably )

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gbm · ‎2025-09-21

Actually what you've designed is a big heater with an annoyingly bright lamp.

My STM32 stuff on github - compact USB device stack and more: https://github.com/gbm-ii/gbmUSBdevice

RendiArdian · ‎2025-09-21

@AScha.3

@gbm

Okay, done, thanks but...,

What about the T1,T2,T3 transistor type ?and, is my design will run correctly ?

Can you help me to test my design with yours Simulator ? What is the max. voltage output ?

Peter BENSCH · ‎2025-09-21

@RendiArdian

The schematic shows a current regulator that uses the potentiometer as a shunt. However, if your output parameters are actually 19V, 20A (even though you have drawn 1.9V), there would have to be 20,000V at the 1k potentiometer (20A * 1k = 20kV).

Please explain what your schematic is supposed to do or what you are connecting there, because (at least) something about it is not right.

Regards
/Peter

In order to give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.

RendiArdian · ‎2025-09-21

@Peter BENSCH thank you so much for your help, well I see my pot act as a shunt instead as voltage divider. and I guess my 1k pot will give me 13.8 volt at half turn for my Dakai transformer and also can be used to turn my Laptop on at max. turn.